Cold Seals Generally
Cold seals are known. Cold seals are also infamous in plastic bag manufacture. Some explanation is in order.
When plastic was first considered as a bag material, difficulty was encountered in sealing such bags. The desired seal was the so-called "hot seal." In such a hot seal, two layers of plastic were sealed together under a temperature and pressure where the molecular structure of the two bag layers permanently bonded and fused together.
A permanent "hot seal" is easy to identify. If one tries to tear apart the joined layers of a hot seal on a plastic bag, the seal--being two layers thick--will not part. Instead, either of the two joined layers will separate well before the hot seal itself will separate.
Unfortunately, where insufficient dwell time, insufficient pressure or insufficient temperature is utilized in what is attempted to be a "hot seal", an imperfect hot seal results which is commonly referred to as a cold seal. Such a "cold seal" can be recognized by tearing the cold seal a part. When a cold seal is torn apart, the two joined layers of plastic separate with their structural integrity intact. It is the "cold seal" that fails and tears.
The infamy of "cold seals" relates to the customer public relations disaster, which almost always occurs when a defective "hot seal" opens in the manner of a "cold seal." Simply stated, the customer is usually leaving the store with his plastic bags filled with carefully selected and purchased merchandise. During this departure, the defective "hot seal"--which in reality is a "cold seal"--opens. The merchandise crashes to the floor--usually with some damage.
For the reasons set forth above, the prior art has been stead fast in its avoidance of "cold seals."
Cold seals have found one place where they have utility. Cold sealing of plastic film is a well-known process and has been applied in a multitude of ways in bag stacks to cause the bag plies to stick together in the bag pack and self open the next bag in sequence. This is described in U.S. Pat. No. 5,183,158 to Boyd and U.S. Pat. No. 5,562,580 to Beasley, et al. Both Boyd and Beasley reveal bags that have been corona treated in order to selectively cold seal--or weld--the plastic film layers together in a stack of bags.
It is to be understood that in this use, the "cold seal" does not form a structural element of the bag. In fact it has been the very careful intent of the prior art to avoid cold seals in any structural element of a bag. As will be seen herein, I claim invention in utilizing "cold seals" for the essential "one time opening" of bags fabricated in the lay flat condition to open and square out with a square bottom.
Plastic Bags Generally
Common plastic bag styles used by retailers in fast food chains, supermarkets, and general merchandise, as well as in point-of-purchase applications, are typically of the bottom seal or sideweld variety and have hot seals at these locations.
These bags are usually gusseted along their sides or along the bottom with the open bag mouth at the top. Many of these common bags have carrying handles, usually of the strap variety or die-cut holes. Typical plastic bags used in supermarket applications are about 0.0005 to 0.00065 in gauge; those used in retail merchandise bags are from 0.0005 to 0.0001; fast food bags are usually from 0.0007 to 0.00125, and; those used in point of purchase applications are typically from 0.001 to 0.004 mil thick.
Retailers usually desire to have a bag stand up on its own during clerk bag loading. Usually square bottom paper bags are used instead of plastic bags. Simply stated, square bottom paper bags stand up; plastic bags used in point-of purchase applications typically do not stand up well at all, unless they are a pouch which typically takes on a rounded shape instead of a rectangular shape like boxes.
Common plastic bags have a cost efficiency. Unfortunately, for clerk and customer, such bags have a "use" inefficiency. This "use inefficiency" relates to the multiple steps, which must be undertaken to use such bags.
Common plastic bags when manually put into use usually follow a certain sequence.
First, the clerk's fingers open the bag mouth.
Second, the clerk at one hand grasps one side of the open mouth at the top.
Third, the clerk with the other hand grasps the opposing side of the bag mouth at the top.
Fourth, the bag is pulled upward to capture air and billow open.
Fifth, the clerk's hand is inserted in the bag to "find the bottom" as the bag is placed on the packing surface.
Sixth, once the bottom is found, the hand is withdrawn, and; seventh, the user grasps the merchandise and begins loading the bag.
Variations on this theme may include the shaking of bags to get them open, the support of such bags in the open position from special racks or any of a myriad of other techniques necessary to simultaneously fill and support the bags.
Most common plastic bags are not fabricated with joints and structure to allow the bag to stand up. It would take a user several seconds to open up and put a common plastic bag in the right shape to make it stand up. It is impractical for a user in a high volume retail outlet to do this, as the cost of labor is substantial. This is one key reason most fast food restaurants still use paper bags.
Contrasted with this technique, paper bags when opened are usually set upright and allow the user to place merchandise inside the bag at the bottom. Likewise, when the bags are unloaded at home, again they are capable of standing upright. It is for this store loading convenience, the upright standing paper bags are preferred by clerks and for the home unloading convenience the upright standing paper bags are preferred by customers.
The need for economical square bottom, thin-gauged plastic bags that stand up is well-known. Some 30 plus patents in the field reflect the extreme need, but yet not a single process exists that is cost effective. The cumbersome processes associated with the many alternate methods of creating square bottom, stand-up plastic bags is evident in the bottom seal bag variety of Hansen et al, U.S. Pat. No. 3,988,870 and 4,929,224; Brinkmeier U.S. Pat. No. 3,896,709; La Fleur U.S. Pat. No. 3,915,077 and Platz, U.S. Pat. No. 3,917,159. Others have come closer to an economically viable product with the means illustrated in Ross, U.S. Pat. No. 5,102,384, and Roen U.S. Pat. No. 4,717,262. But as of yet, no process has been anywhere close to the cost effectiveness of current T-shirt manufacturing processes or that of common bottom seal and sideweld plastic bags, all these bags without a "squared out bottom."
In the high-speed bag manufacturing processes used throughout the world, plastic bags are typically made from tube stock. This tube stock is cut out and sealed--either bottom sealed or side welded--as the last step before being packed in a carton.
Placing a square bottom on an already manufactured bag has proven to be costly. To clamp and fold over and/or seal gussets together after a bag has already been cut and sealed from its tube stock in order to create a square bottom bag is not economically viable. As illustrated in the above patents, Ross '384 and Platz '159, this bag forming process requires a costly secondary operation after the bottom sealing process is completed and the bag has been cut free from the tube stock. These processes use a relatively sophisticated grasping and clamping to accomplish the folding process. As defined in Hansen '224, the making these square bottom bags requires placing a mandrel inside the tube prior to cutting and sealing. This too is unreliable and too costly for many reasons. Tube widths vary greatly--a narrow tube would cause the mandrel to lock up inside the tube and then break the tube--a slightly wider tube would result in not having a properly formed bag. Further, this process requires narrow plastic tubes instead of the wider, more efficient ones used on 3-5 lane machines. Finally, the bag machine speeds are slow. These three factors drive up the prices of the bags making them impractical when compared to paper or other alternative technologies.
La Fleur, '077, reveals angle sealing that is more cost effective than the three others listed above, but is still too costly for bags made on modern, high-speed bag equipment that typically runs 3-5 lanes across and in speeds in excess of 125 cycles per minute. Trying to simultaneously control the heat sealing (or any folding means, for that matter) of 12 to 24 side gusset pairs per cycle results in either substantially reducing the machine's speed or a highly unreliable, inconsistent outcome at best. The inconsistent output results in uneven seals, which then causes irregular, cockeyed bag bottoms once they are opened and a user tries to stand them up.
All of the above bag styles will cost substantially more to produce than common plastic bag styles, generally as much as 20-30%, even up to 300% more, depending upon size. Only the Roen '262 bag product can produce an economically cost-effective bag but is limited to side weld bag production and is not practical on smaller bags running 3-5 lanes across.
Of particular importance in the field of plastics packaging is that heat sealing plastic bags--whether that be the angle seals as described in La Fleur '077 or a common bottom sealing process--is typically accomplished at temperatures of around 500 F. degrees. This is because at high cycling speeds, it is desirable to seal the plastic film as fast as possible, in which hot temperatures are required. In order to seal effectively at hot temperatures in the 500-degree range, an insulating material such as Teflon is placed between the plastic material and the 500-degree hot heat seal bar, preventing the molten plastic from sticking to the metallic heat seal bar. This would be the normal, traditional means of heat sealing plastic film products used by virtually every major, high-volume manufacturer in the U.S. and most likely the world. A means of sealing plastic film for any variety of uses, including bottom sealing, side welding or angle-sealing that can improve upon this means would be of tremendous value.
Another methodology of creating seals at the angular bottom portions of squared out plastic bags of the side gussets is revealed in U.S. Pat. No. 5,195,829 to Watkins in which adhesive is used to bond the triangular portions of a square bottom together. Even use of adhesive is possible in the popcorn bags described in the '829 patent which is a form and fill operation.
It is important to note that angle seal technology can also produce uneven or even incomplete seals, which may result in irregular bag bottoms once they are opened and placed into use.